A friend and I are moving out to Colorado for a year or maybe more... We're researching cities right now. We're 23 yr old females, from St. Louis, MO, flexible with our jobs right now (just taking some time off to travel and see the US)--will be working...

Answer:

Those are all great cities that you have mentioned. However for diversity, prices, and a large city...

As a reference, Ralph Nader beat George W. Bush in both Cambridge, MA and Berkeley, CA (and maybe New Haven, CT too, IIRC) But it's a lot more complex than that; % voting for Democrats isn't the best metric since there are lots of conservative Democrats...